Andy - how did you get on? My car has been at the dealer's for a week. After having it 1 day they rang and told me there was nothing wrong with it but that a "senior technician" wanted to take a look. 3 days later they told me the same as yours - faulty sensor. Ordered, painted, and fitted yesterday. Collected car last night (after rain) and all working fine - hurrah (or so I thought...).
This morning (rained overnight here) - back to square 1 :-(
Have just booked it in for the 6th time at the dealer next Monday, and have also phoned SEAT UK customer services and logged a complaint.
How did you get on with yours? I can't believe how difficult it seems to be to get this resolved. Such a shame too as the rest of the car is great. Having had a BOL Skoda Fabia for the last week as a courtesy car I can really appreciate the Exeo now....!